Boiler zones - quest for high flow rates

[MNBobcat]

Hi everyone.

I have an outdoor wood furnace located 275 feet from my house. I ran 1 1/4 thermopex between the house and the boiler. I'm trying to design the indoor plumbing such that I don't kill the flow rate that the larger 1 1/4 pex provides. My round-trip loop may be close to 600 feet.

One of my concerns is that the forced air furnace HX will likely have 3/4" tubing. I'm assuming that going from 1 1/4 down to the 3/4 will kill my flow rate if I run everything in series.

What i would like to do is try and maintain a continuous 1 1/4 loop between the boiler and the house and pull off whatever I need for my various "zones".

I have a plate heat exchanger with 1 1/4 inlet and outlets already purchased for heating my domestic hot water (2 80 gallon electric water heaters)

I also want to put a modine heater in my attached garage. So for sure I'll be drawing BTUs for the DHW, the house furnace and the garage furnace. Down the road, I might want to add a zone for heating 1 or 2 other rooms in the house.

How would you plumb this with the above in mind?

 

[Gooserider]

Do a search on "Primary / Secondary" - I think that would be your best approach... Essentially a P/S system consists of a main loop that just goes out from the boiler and back, possibly hitting a storage tank, but no major loads. Each load (or possibly a set of loads) is tied to the primary loop with a pair of "closely spaced tees" - two tees that are spaced less than 4-6 pipe diameters apart - basically as close as the fittings will let you be, and a pump that will pull water out of the primary loop at the first tee, and return it at the second as needed by the load. This puts virtually no restriction on the main loop, which is what you are after.

Theory says that because the tees are so close together you shouldn't get any flow in the loop if the pump is off - practice says you end up with a little, and can also get thermally induced "ghost flow" so you will likely want to use a pump w/ a flow check in it, or other such valves to stop that flow...

The problem is that the temperature available to loops later in the main loop will be potentially lower and variable than what the first loop gets because of the heat pulled off by each loop in turn - this may or may not be a problem depending on your setup. If it is, there are also ways to run the main loop through several parallel branches, and pull off the branches (look for Parallel P/S systems)

If you don't find what you are after in the forums, there are several good Siegenthaler articles that show P/S systems, or look in the Caleffi website for their "Idraulica" webzine (link in the Tidbits sticky) for some example layouts...

Gooserider